Fuses are frequently used to reconfigure memory and logic circuitry. For example, in dynamic or static memory chips, defective memory cells or circuitry may be replaced by selectively blowing (destroying) fuses associated with the defective circuitry while activating redundant circuitry to form new circuitry. This circuit rerouting technique using selectively destroyed fuse links contributes to enhanced yields without the necessity of scrapping defective process wafers.
Generally, fuse links, made of a conductive material may be destroyed to form an open circuit by passing an excessive electrical current through the circuitry which melts the fuse link or otherwise increases the resistance of the fuse link to effectively block conduction below a certain voltage.
Although both electrical current and laser ablation have been used to blow fuses, passing of electrical current is preferred in certain situations since a pre-determined current may be programmed and fuse links selected with a greater degree of facility compared to laser ablation operations. For example, programmed electrical current used to blow selected fuses may facilitate field operations to repair devices and trim analog devices for suitable operation.
One problem with programmable fuses of the prior art is the tendency for processing variables to result in a wide variation of electrical resistances in the fuses. As a result, frequently, the fuse electrical resistance is formed out of specification and the programmed Voltage and current is either too large for the fuse resistance, causing possible damage to the circuitry, or too small, resulting in unblown fuses.
As device sizes decrease, including the fuse link dimension, resistance variations due to processing variables such as altered critical dimension of the fuse link as well as material inhomogeneities increasingly result in a wide distribution of fuse link electrical resistances, reducing the reliability of fuse blowing operations and increasing the possibility of damage to the circuitry.
Therefore, there is a need in the semiconductor processing art to develop an improved fuse-link structure and method of using the same in a fuse blowing process such that a fuse-link structure is formed with a predetermined electrical resistance variation and consequently reliably blown in a fuse blowing process.
It is therefore an object of the invention to develop an improved fuse-link structure and method of using the same in a fuse blowing process such that a fuse-link structure is formed with a predetermined electrical resistance variation and consequently reliably blown in a fuse blowing process, in addition to overcoming other shortcomings of the prior art.